The proposed studies are designed to further our understanding of the factors which regulate erythropoietin production from both kidneys and extrarenal sites. The amount of eryhropoietin in homogenates of various organs and in the plasma will be assayed by a bioassay. The effects of various hormones, protein deprivations and various surgical procedures which cause renal hypertrophy on these parameters will be determined. Also, the effects of bile duct ligation, partial hepatectomy, CC14 administration, and angiotensin infusion on extrarenal erythropoietin production and on Kupffer cell, hepatocyte, bild duct epithelium, and hepatic and systemic blood flow will be measured. Rats made uremic by removal of 5/6 of their renal mass will be used as models for the study of conditions which produce chronic changes in extrarenal erythropoietin production.